Microlithographic projection exposure apparatuses are used for the manufacture of microstructured components such as for example integrated circuits or liquid crystal displays (LCDs). A projection exposure apparatus of this kind includes an illumination system and a projection objective. In the microlithography process, an image of a mask (commonly referred to as a reticle) that is illuminated via the illumination system is projected via the projection objective onto a substrate (for example a silicon wafer) which is coated with a light-sensitive coating layer (photoresist) and is arranged in the image plane of the projection objective, whereby the mask structure is transferred to the light-sensitive coating of the substrate.
As is known, the image contrast in the microlithography process can be significantly improved if the mask is illuminated with linearly polarized light, wherein it is of advantage if the preferred direction of the linear polarization is parallel to the lengthwise direction of the grid structures that are present on the mask. In the illumination with polarized light, it is also desirable that the polarization distribution be as constant as possible over the entire reticle field in order to achieve a constant image contrast and thus a defect-free image of the grid structures. However, a problem is encountered here in that the light falling on the mask has previously traveled over different ray paths in the illumination system, where an originally existing polarization distribution (of light that was generally of linear polarization when it entered the illumination system) has been changed to different degrees on the different ray paths by polarization-influencing effects (e.g., by stress-induced birefringence caused by components of mounting devices in the material of the optical components such as lenses, or by polarization-influencing effects of dielectric layers, etc.).